Sorption of hydrocarbons by activated carbon



Oct. 16, 1951 J. A. PATTERSON ET AL 2,571,936

SORPTION OF HYDROCARBONS BY ACTIVATED CARBON Filed March 6, 1948 4Sheets-Sheet l f-JJ CooLasz Jerome 1D. mor Acnr?- Johrz @.Pebersgcan.sn've't'ors ExCLbborr/Leg Oct. 16, 1951 1. A. PATTERSON r-:TAL 2,571,936

SORPTIYON OF HYDOCARBONS BY ACTIVATED CARBON 4 Sheets-Sheet 2 FiledMarch 6, 1948 vuu All Om N -..gk

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Oct. 16, 1951 J. A. PATTERSON ET A1. 2,571,936

,soRPTIoN oF HYDRocARBoNs BY ACTIVATED CARBON 4 Sheets-Sheet 5 EFW Y LIiwmdomm@ Filed March 6, 1948 Oct. 16, 1951 J. A. PATTERSON ET AL2,571,936

soRPTIoN oF HYnRocARBoNs BY ACTIVATED CARBON Jrome P mor cu2 @rdmapaafgoa. 5mm-ifo F93 @MM Clbborrze Patented Oct. 16, 1951.

SORPTION OF HYDROCARBONS BY ACTIVATED CARBON John'A. Patterson, Beverly,and Jerome P. Morgan, Maplcwood, N. J., assignors to Standard OilDevelopment Company, a corporation of Delaware Application March 6,1948, Serial No. 13,414

1 Claim.

This invention relates to improvements in the sorption of hydrocarbonsby solids and relates particularly to improvements in the sorption andpurification of cyclohexane and other hydrocarbons.

Activated carbon, activated charcoal, silica gel and other adsorptionsolids have been used to selectively adsorb various hydrocarbons as theadsorptive aillnity of the solids have been found to generally vary inthe following decreasing order:

1. Aromatics 2. Oleflns 3. Naphthenes 4. Paraillns When a solution of anaromatic hydrocarbon with a parailin and a naphthene is filtered througha column of solid adsorbent, the rst portion of the adsorbent comes intocontact with successive portions of solution having the initialconcentration of aromatic hydrocarbons. This layer of adsorbent soonreaches a state of equilibrium between the aromatic hydrocarbons in thesolution of the original concentration and the amount of aromatichydrocarbons adsorbed per unit quantity of adsorbent. As the solutionmoves down through the bed, successive layers of adsorbent come intocontact and into equilibrium with solution of the initial concentration.Thus, extending downward from the top layer of adsorbent, a zone isformed in which the adsorbed aromatic hydrocarbon is in equilibrium withsolution of the initial concentration, which fills the microscopicinterstices of the adsorbent. With continued introduction of solution`at the top of the column this equilibrium zone extends farther andfarther down the tube, forcing the aromatic-free material ahead of itwith (if the iiltration is not too rapid) a comparatively narrow regionbetween the equilibrium zone and the aromatic-free zone. Finally theequilibrium zone reaches the bottom or last layer of adsorbent, and atthis point solution containing the initial `concentration of aromatichydrocarbons just begins to emerge as ltrate from the bottom of thecolumn of adsorbent.

It is apparent that the treatment of'a solution of an aromatichydrocarbon in a parailin and naphthene in the manner just described mayyield a portion of the charge as aromatic-free material, but that aquantitative separation of parailinic hydrocarbons is not possible bythis process alone.

An object of this invention is to separate parafiins and naphthenes fromthe aromatics, and

(Cl. 26o-666) also from each other in substantially pure form. Theboiling points of the various hydrocarbons having from 6-7 carbon atomsto the molecule. range from 49.7 C. to 1-l5 C. Cyclohexane boils at 80.8C., benzene boils at 80.2 C., and the azeotrope of these twohydrocarbons boils at 77.5 C. Although in distilling a mixture of Cs toC1 hydrocarbons, various azeotropes will be formed, therefore, infollowing out this method of separating cyclohexane, a. cut boilingbetween 70-85 C., will contain the major fraction of cyclohexane.together with paraiiins, aromatics, olefins and naphthenes. This cut canthen be separated in a plurality of stages of adsorption and desorption.The separation may be carried out in either a liquid or vapor phasesystem.

'I'he invention will be more fully understood by reading the followingdescription with reference to the accompanying drawing.

Fig. 1 showing the ilow of materials in a vapor phase system.

Fig. 2 showing a modification of the said system.

Fig. 3 showing a further modification of the ilow plan.

Fig. 4 showing a further modification oi' stripping in the desorptionsystem, and

Fig. 5 showing a system in which paraiilns and nanhthenes are separated.

Referring to Fig. l, an example of a vapor phase operation, a Ce to Cvcut, preferably one boiling l between 7085 C., is introduced into alower -adsorption level. An adsorbent such as activated carbon of200-500 mesh is passed into the top of the adsorber zone 2 by means ofpipe 5 which may or may not be a standpipe. The Cs to C1 cut is passedin countercurrent iiow to the adsorbent and from the upper part ofadsorber zone, a, substantially aromaticand olefin-free fraction of theCe to Cv hydrocarbons is removed through pipe 6. The adsorbent with thearomatics, and olens adsorbed therein is passed to a stripper zoneprovided with a steam coil 8 and superheated steam is supplied by meansof pipe 9, and the aromatics and olefins are desorbed from the carbonand removed through pipe Ill, at the upper part of. the stripper 1. Anessentially dry fraction of the aromatics and olefins may be refluxed tothe bottom of the adsorber 2, by means of pipe I I to desorb any of thenaphthenes and paraillns that may be held by the adsorbent at the lowerpart of the adsorber zone 2 or an internal reilux is obtained bymaintaining a back pressure on productl stream. The adsorbent free ofhydrocarbons is then passed from the bottom of the stripper zone 1through pipe 5 and through cooler I to the upper part of adsorber 2. Thehydrocarbons removed through pipe B are passed to a. second adsorberzone I2 and then passed in counter current flow to an adsorbent suppliedto the adsorber by means of pipe I3. Heat regulating coils I 4 areprovided in the adsorber zone I2 which may be provided with plates orbailles. The hydrocarbon fraction after passing in countercurrent ow tothe adsorbent in adsorber zone I2, which may likewise be activatedcarbon, is removed through pipe I5 and is substantially a paralnfraction. The adsorbent is passed from the adsorber zone I2, to astripper zone I6 where it is stripped of its hydrocarbons by means ofsuperheated steam supplied through pipe I1 and coil I8. The hydrocarbonsconsisting of substantially pure naphthenes of at least 80%concentration, is removed through pipe I9. A fraction of this stream maybe refluxed through pipe 20 to the bottom of adsorber I2 to desorb anyparaflins that will be present in the adsorbent, passed to stripper I6.The naphthene fraction removed through pipe I 9 can be readilyfractionally distilled to obtain pure cyclohexane. The adsorbent free ofthe naphthenes is then recycled through pipe I3 to the top of adsorberI2, after passing through cooler 2|.

Referring to Fig. 2, Cs to Cv hydrocarbon mixture preferably of aboiling range of 70-85 C. is passed through pipe 3| to the lower part ofan adsorber 32, which adsorber may be provided with battles or plates.The hydrocarbon mixture is then passed in countercurrent flow to a solidadsorbent, such as activated carbon. or activated charcoal which isintroduced into the adsorber by means of pipe 33. Adsorbent circulationis regulated so that substantially pure parafnns of at least 80%concentration are removed through pipe 34. The adsorbent with thenaphthenes, olens or aromatics adsorbed or occluded is passed fromadsorber 32 by pipe 35 to desorber 36 where it is heated to desorbsubstantially all of the naphthenes without disturbing the bulk of theadsorbed olefins and aromatics. The desorbed naphenes are removed bymeans of pipe 31 from the desorber and an essentially dry fraction ofnaphthenes is refluxed to the bottom of adsorber 32 by means of pipe 38to selectively displace any paraffin remaining on the adsorbent.Superheated steam for removing the naphthenes from the adsorbent isprovided by means of pipe 39 to the bottom of desorber 36. Followingdesorption of the naphthenes the powdered or nelv divided adsorbent isthen removed by means of pipe 40 to the top of a second desorber 4I towhich superheated steam is supplied by means of pine 42 to desorbsubstantially all of the olens which are removed by means of pipe 43,and a dry fraction is refluxed to the bottom of desorber 4I by means ofpipe 44, The residual adsorbent with the aromatics as the adsorbate isthen passed by means of pipe 45 to the top of a third desorber 46 towhich superheated steam is supplied by means of pipe 41 to expel all ofthe remaining hydrocarbons in the adsorber which are removed throughpipe 48, and the essentially dry fraction being refluxed to the bottomof desorber 4I by means of pipe 49. The hot, stripped adsorbent is thenremoved through pipe 33 and recycled to the top of adsorber 32 afterpassing through cooler 49.

Referring to Fig. 3, a Cs to C1 hydrocarbon mixture containingcyclohexane' is passed through pipe 50 to the lower part of an adsorber5I and passed in countercurrent flow to the solid adsorbent such asactivated carbon introduced into the top of the adsorber by means ofpipe 52. The

temperatures of the hydrocarbon mixture and the solid adsorbent, as Wellas the amount of the latter circulated are regulated so thatsubstantially all of the naphthenes, olens and aromatics are adsorbed.The unadsorbed hydrocarbon, that is, the paraffin fraction, is removedfrom the adsorber 5I by means of pipe 53. The solid adsorbent with thenaphthenes, olens and aromatics adsorbed therein is passed through pipe54 to the top of a stripping tower 55 which is provided with a pluralityof plates, and superheated steam is introduced above the top plate 56 bymeans of pipe 51, where naphthenes are expelled from the solid adsorbentand removed by a side stream through pipe 58, an essentially dryfraction being renuxed to the bottom of the adsorber 5I, by means ofpipe 59, to remove any parans that may remain adsorbed on the solidadsorbent. Superheated steam is provided by means of pipe 60 to the topof plate El, olefns thus desorbed from the solid adsorbent are removedthrough pipe 62. A stream of superheated steam is passed through pipe E3to the lower part of the tower 55, aromatics are thus desorbed andremoved from the stripping tower by means of pipe 63. The hot strippedadsorbent is then removed from the bottom of tower 55 through pipe 66,and after passing through cooler 65 are recycled to the top of theadsorber 5I. The naphthene fraction which is removed through pipe 58 maybe readily fractionaily distilled to obtain pure cyclohexane.

Referring to Fig. 4, a Cs to C7 hydrocarbon mixture is passed throughpipe 10 to an adsorber 1I, where it passes in countercurrent now to asolid adsorbent such as activated carbon introduced to the top of thetower by means of pipe 12. The temperature and quantity of solidadsorbent are regulated to absorb the oleflns and the aromaticfractions, and the unabsorbed fraction, consisting of parailins andnaphthenes is removed through pipe 13 from the adsorber 1I. The solidadsorbent with the olens and aromatics therein is passed through pipe 14to top of 'tower 15. The lower part of this tower is supplied withsuperheated steam by means of pipe 1B for desorbing and stripping offthe olens which are in turn removed through pipe 11, a dry fraction ofthe olens being recycled by means of pipe 18 to the lowerpart of theadsorber 1I. Solid adsorbent with aromatics adsorbed on it is thenremoved through pipe 19 to desorber 80 to which superheated steam isprovided by means of pipe BI to expel the residual aromatic fraction ofthe solid adsorbent which is removed through pipe B2, a part of thefraction may be passed through pipe 83 and refluxed to desorber 15. Thehot, stripped, solid adsorbent is removed through pipe 85 from desorber30, and after passing through cooler 84 is recycled to the top of theadsorber 1I.

The parailn and naphthene fraction is removed by pipe 13, to anotheradsorber 8B Where it passes in countercurrent flow to a solid adsorbent,which likewise may be activated carbon. Said adsorbent is passed intoadsorber 86 by means of pipe 94. A paraffin fraction substantially freeof naphthenes is removed through pipe 81 from the adsorber 86. The solidadsorbthene fraction removed through pipe 9| is thenl fractionallydistilled to recover cyclohexane.

Referring to Fig. 5, a C6 to C7 mixture is passed by pipe into adsorber|0| where it passes in countercurrent iiow to a solid absorbentintroduced into the adsorber |0| by means of pipe |02. The unabsorbedparafln fraction is removed frorn the adsorber |0| by means of pipe |03.Plates |04 and |05 are provided in the adsorber, and from the bottom ofplate |04, a naphthene fraction is removed as a side stream by means ofpipe |06. As the solid adsorbent passes further down in the adsorber |0|and is gradually heated at some point below the feed plate bysuperheated steam provided for desorbing and stripping purposes by meansof pipe |09 and coil ||0. The desorbed olefins are removed by pipe |01as a side stream. The aromatics desorbed in the bottom section of thestripper, are removed as a side stream by means of pipe |08. Thetemperature gradient and the back pressure on the side streams is soregulated that the oletins substantially paraiiinand naphthene-free areremoved through pipe |01 and the naphthenes substantially paraffin-freeare removed through pipe |06. The hot, stripped solid adsorbent isremoved from the bottom of the tower |0| by means of pipe |02 and afterpassing through cooler is recycled to tower |0I. Cyclohexane isrecovered in concentrated form by conventional means from the naphthenefraction. The other fractions may be treated to recover valuableproducts if desirable. Temperatures up to 110 to 120 F. are maintainedduring the adsorption. Room temperatures are preferably used. The

adsorbent is heated between 300 and 550 F. to

bon downwardly through an adsorption Zone, itroducing the Ce-Cvhydrocarbon mixture in vapor phase into a lower portion of theadsorption zone, contacting the ascending hydrocarbon vaporscountercurrently with the descending carbon whereby the cyclohexane,olen and aromatic hydrocarbons become preferentially adsorbed on thecarbon, removing unadsorbed hydrocarbons from an upper portion of theadsorption zone, withdrawing rich activated carbon containing adsorbedthereon cyclohexane, olefin and aromatic hydrocarbons from theadsorption zone and passing it downwardly successively through a. rst,second and third desorption zone, heating the activated rich carbon inthe rst desorption zone to a first desorption zone to a first desorptiontemperature of about 300 F. to liberate therefrom a cyclohexane stream,returning a portion of the cyclohexane as reiiux to a lower portion ofthe adsorption zone, heating the activated carbon freed of cyclohexanebut containing adsorbed olens and aromatics thereon in the seconddesorption zone at a temperature higher than that in the firstdesorption zone, recovering a vapor stream of olen hydrocarbons from theseconddesorption zone, returning a portion of the withdrawn olefinhydrocarbons to the rst desorption zone, heating the activated carboncontaining adsorbed aromatic hydrocarbons in a third desorption zone ata higher temperature than in the second desorption zone but not above550 F. to remove the aromatic hydrocarbons from the carbon, withdrawingthe aromatic hydrocarbons from-the third desorption zone and returning aportion thereof tothe Second desorption zone.

JOHN A. PATTERSON. JEROME P. MORGAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Dat 2,384,311 Kearby Sept. 4, 19452,398,101 v Lipkin Apr. 9. 1946 2,470,339 Claussen et al May 17, 1949OTHER REFERENCES Hirschler et al., Ind. Eng. Chem., v01. 39, 1585- 96(1947) Mair, Jour. Res. Nat. Bur. Stand., vol. 34, 435- 4.51 1945).

Turner Petroleum Renner. vol 22, 98 [1401-102 [144] (1943).

